I think you're taking simple comparisons out of context.But an 11 inch MBA isn't a tablet its a laptop and 40g in laptop mode is not only insignificant it's irrelevant. I wouldn't use an SP3 as a tablet with the keyboard attached, further more 1.71 is not closer to 2 than 1.5. These weak and false arguments fall flat.
An iPad is about 470g so very much lighter for instance and smaller and may have been a better comparison. The newer one is 437g, almost half the weight.
Some SP3 users use their machines for everything but other's like me don't, for reasons mentioned.
There is definitely a market for a Broadwell M based Surface in an ultra compact form factor.
You can't have everything though, compromises all around if you want the holy grail of one device for everything, something I've never myself believed in and hence the debate.